Technical Abstract:
The crop evapotranspiration (ETc) was measured using two methods: Penman-Monteith (P-M) with variable surface resistance (rs) and aerodynamic resistance (ra), and drainage lysimeters. The two common bean genotypes used in this study were Morales and SER 16, both having type II plant architecture, but differing in their response to drought stress. The experiment was performed under semi-arid climatic conditions at the University of Puerto Rico. Climatic data from the field was collected every 10 seconds using four automatic weather stations. The lysimeter ETc was measured two times per week and the reference evapotranspiration (ETo) was measured using the P-M method. A large, well-watered grass area located adjacent to the experimental plot was used for reference evapotranspiration. One-half of the experimental plot experienced water-limiting conditions beginning with the R1 developmental phase (one blossom open at any node) and ending with harvest. The Kc values were 0.4 for Morales and 0.2 for SER 16 at the V8 stage (last vegetative stage), 1.0 for Morales and 0.8 for SER 16 at R7 stage (oldest pods have developed seeds), and 0.9 for Morales and 0.7 for SER 16 at the mature pod stage. The rs for non-limited water was 1167.2 sm-1 for Morales and 8359.0 sm-1 for SER 16 at the V8 stage, 150 sm-1 for Morales and 230 sm-1 for SER 16 at the R7 stage, and 138 sm-1 for Morales and 417 sm-1 for SER 16 at the mature pod stage. Total ETc measured with the lysimeters under non-limited water conditions was 367.8 mm for Morales and 322 mm for SER 16, and for limited water was 331 mm for Morales and 276 mm for SER 16. The results showed that limiting water at the R1 stage induced reduction in dry matter accumulation, seeds per pod, and seed yield.